nest egg
noun /ˈnest eɡ/
  /ˈnest eɡ/
(informal)- a sum of money that you save to use in the future备用的钱;储备金 - Over the years she had built up a nice little nest egg for her retirement.这些年来,她为自己的退休积累了一笔可观的积蓄。 
 
- Over the years she had built up a nice little nest egg for her retirement.